<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>圆的计算</title>
</head>
<body>
<input type="text" placeholder="半径" id="a">
<input type="text" placeholder="周长" id="b">
<input type="text" placeholder="面积" id="c">

<script>


    var p = prompt("请输入圆的半径");

    var pi= Math.PI;

    document.querySelector("#a").value = p;
    document.querySelector("#b").value = p*2*pi;
    document.querySelector("#c").value = pi*p*p;
</script>
</body>
</html>